Container for transporting thermally hot intensely radioactive material



Jan. 28, 1964 J w ALLEN Filed May 3, 1960 3,119,933 CONTAINER FORTRANSPORTING THERMALLY HOT INTENSELY RADIOACTIVE MATERIAL 4 Sheets-Sheet1 INVENTOR. 58 J HN W. ALLEN IIL-FEHE- W SEARS ROOM J. w. ALLEN3,119,933

4 Sheets-Sheet 2 N\ m\ wm mm mW IL 1mm m wn Nn A W CONTAINER FORTRANSPORTING THERMALLY HOT INTENSELY RADIOACTIVE MATERIAL I L N/ Jan.28, 1964 Filed May 3, 1960 v Q m NV wv l N i Jan. 28, 1964 J. w. ALLEN3,119,933

CONTAINER FOR TRANSPORTING THERMALLY HOT INTENSELY RADIOACTIVE MATERIALFiled May 3, 1960 4 Sheets-Sheet I5 V i Y INVENTOR.

JOHN W. ALLEN J. W. ALLEN CONTAINER FOR TRANSPORTING THERMALLY HOTINTENSELY RADIOACTIVE MATERIAL Jan. 28, 1964 4 Sheets-Sheet 4 Filed May3, 1960 IN VEN TOR.

JOHN W. ALLEN United States Patent 3,119,933 CONTAINER FQR TRANSPORTINGTHERMALLY HOT INTENSELY RADIOACTIVE MATERIAL John W. Allen, La Grange,11L, assignor to Stanray Corporation, Chicago, 1th, a corporation ofDelaware Filed May 3, 1960, Ser. No. 26,468 6 Claims. (Cl. 250-408) Thisinvention relates to containers for transporting radioactive materials,more particularly, it relates to containers of minimal dimensions andweight yet having high strength for transporting intensely radioactivematerials which are exothermal and which may encounter temperatures fromheat generated internally of several hundred degrees fahrenheit duringtransport.

This application is a continuation in part of my copending United Statespatent application, Serial Number 783,474, filed December 29, 1958,titled Container for Radioactive Material, John W. Allen, inventor, nowabandoned.

As disclosed in the aforesaid patent application there is need forcontainers suitable for the shipment of intensely radioactive materialswhich may be exothermal and even under favorable cooling conditions mayreach temperatures of several hundred degrees Fahrenheit. Such materialsare, for instance, encountered as waste products in the form of spentnuclear reactor fuel elements.

It is necessary to transport intensely radio-active and highlyexothermal nuclear reactor waste products over common carriertransportation lines such as truck and rail routes. These materials arecarried into and through populated areas and are not infrequently leftstanding on sidings and in traflic where the general public could, as

they pass nearby, be exposed to the hazards of radiation and thermalheat burns excepting for the protection afforded by the container inwhich the dangerous radioactive material is being carried. The weightand dimensions of suitable containers for transporting radio-activematerials are limited by economic considerations as Well as theawkwardness of manipulating and conveying immense heavy radiation shieldstructures. In addition to the cost and physical difficulty of conveyingradio-active materials in a shielded container, the problem of theintegrity of the container and the integrity of the radiation shieldunder the stress of difierential heating of the various parts of thecontainer and the mechanical shock attendant in loading, unloading andhigh speed travel across the country must be solved. The more dense, andtherefore, better gamma ray radiation attenuating materials, such aslead and metal loaded concrete are generally deficient in strength andin heat conductivity; the stronger materials, such as carbon steel,aluminum alloy and copper are generally good heat conductors but notnecessarily superior gamma ray radiation attenuators and are subject tosevere dimensional disturbances due to large coetficients of heatexpansion. Hence, a composite structure is required which willincorporate the best features of various materials for the constructionof a suitable radiation shielding container, achieve a minimal weightconfiguration, and provide design which assures complete radiationshielding under all circumstances of stress.

Radioactive waste products resulting from the fission of uranium 235such as are found in spent nuclear reactor fuel rods contain, forinstance, over two hundred fission fragments nearly all of which areradioactive and emit beta rays, neutrons and gamma rays. A large portionof these fission fragments emit both beta and gamma rays as delayedfission gamma radiation. The proportion of neutrons emitted by thesedelayed fission reactions is a very small percentage of the entireradiation. Neutrons are readily captured in most environments, hence insmall 3,ll9,933 Patented Jan. 28, 1964 concentrations do not constitutea penetration radiation, although their capture will in some iosotopesgive rise to (N, 'y) reactions from which the resultant gamma radiationis highly penetrating. The energy of most of the gamma radiation fromdelayed fission reactions is less than 2 mev., however, a small butsignificant percentage is of much higher energy and therefore createsextremely penetrating radiation. The resulting beta radiation fallsbetween 1.2 and 3 mev. Beta rays are light particles which are easilyscattered and hence do not form penetrating rays; they carryconsiderable energy and constitute ionizing radiation which form ionpairs that in themselves are not a radiation hazard. Accordingly,shielding structures for radioactive Waste such as spent nuclear reactorfuel rods need only assure absorption of the gamma rays present; theneutrons and beta particles will be substantially totally shielded byany suitable gamma shield structure. A satisfactory gamma ray shieldmust absorb the gamma photons from the primary source as well asinelastically scattered gamma and gamma photons emitted by nuclei in theshield as a result of interaction with neutrons in (N, 'y) reactions.

The absorption of gamma ray radiation in shielding material isaccomplished by photoel e c tric interaction, compton effect, and bypair production. All of these mechanisms are energy dependent. Theindividual linear absorption coethcients of each absorption mechanismvary considerably with the energy of the incident rays; accordingly, thesum of these three absorption coefficients varies in non-linearrelationship with the energy of the incident radiation. The least alsorption of gamma rays in most shielding materials occurs in thevicinity of 4 mev. energy incident radiation. The various absorbermaterials such as might be utilized in a radiation shield each possessesa characteristic gamma ray absorption coefficient curve which is energydependent.

Because of the considerable complexity of the many parameters which mustbe considered in computing the thickness of an appropriate radiationshield certain simplifying assumptions may be made to aid the designer.One of these is the relaxation length of a material; that is theapproximate linear length or thickness of a shielding material requiredto reduce the intensity of the incident radiation (assumed to be about 4mev. energy photons) by a factor of 1/e or 1/ 2.72. The decrease inradiation intensity through a shield is exponential, hence no simpleformula will relate the shield effectiveness to the strength of theradiation source and the dimensions and character of the shieldmaterial. The linear absorption coefiicient N given in cm. units relatesthe thickness, x, of a shield, for any particular energy of gammaradiation to the intensity of the radiation 1 and the intensity ofradiation I at x cm. through the shield by the relationship: I =I e Theabove information and additional data relating to specific shieldmaterials is published in numerous places in the literature, particularreference is made to Principles of Nuclear Reactor En gineering, SamuelGlasstone, New York, 1955.

Much thermal energy is given oif by radioactive material andconsiderable thermal heat is generated by the capture of nuclearradiation in a shield material. One specific example of the highexothermal character of radioactive waste in spent reactor fuel rods isindicated by the fact that approximately 100,000 B.t.u. per hour areemitted by a bundle of only thirty-two such fuel rods. A container inwhich to carry these rods must therefore dissipate this much thermalenergy to maintain temperature equilibrium. Such an amount of heatcompares with the heat capacity of a household furnace. Failure todissipate the evolved thermal energy will cause an abrupt rise intemperature of the container and its contents and ultimately failure ofthe radiation shielding container.

It is therefore an object of this invention to provide a minimaldimension safe container for storing and transporting intenselyradioactive and highly exothermal radioactive waste products.

It is also an object of this invention to provide a minimal weightcontainer adapted to dissipate sizeable quantities of thermal heat andsimultaneously provide radiation shielding without risk of openings inthe radiation shielding structure due to thermal stresses induced bydifferential heating of various parts of the container.

It is still another object of this invention to provide a containerwhich is extremely rugged, suitable for transporting intenselyradioactive materials which will assure safe biological radiation levelsabout its exterior during all predictable circumstances while thecontainer is in transport.

This and other objects and advantages of my invention will be apparentfrom the folowing description, spec fications, drawings and claims.

My invention comprises, briefly, a minimum dimension container adaptedfor transporting intensely radioactive, highly exothermic materialcomprising an inner arid an outer shell in spaced relationship, webbedsections therebetween, the shells and web being made of high strengthmaterial with high coefficient of heat conductivity, high densityradiation shielding material positioned in the voids between the shells,whereby the radiation shielding inrtegrity of the container is preservedregardless of the temperature of thec omponent parts of the container,the heat being removed from the interior of the inner shell byconduction through the webs to the outer surface of the outer shellwhere it is dissipated, and the radiation being attenuated by passingtransversely through the high density shielding material members orlongitudinally through the web sections.

My invention is described and illustrated by the following drawings andspecifications:

FIGURE 1 is a partly cut-away perspective view of a preferred embodimentof my invention;

FIGURE 2 is a transverse cross sectional view of the embodiment shown inFIGURE 1;

FIGURE 3 is a longitudinal cross sectional view of the embodiment shownin FIGURES 1 and 2;

FIGURE 4 is a fragmentary view showing certain structural details of theembodiment illustrated in FIG- URE 1;

FIGURE 5 is a perspective cut-away view of a second embodiment of myinvention;

FIGURE 6 is a fragmentary cross sectional view of a specific embodimentof my invention very similar to that illustrated in FIGURES l, 2 and 3;

FIGURE 7 is a fragmentary cross sectional view of another specificembodiment of my invention;

FIGURES 8 and 9 are drawings copied in detail from the original parentpatent application, Serial No. 783,474, now abandoned, thereindesignated FIGURES 1 and 2, which illustrate the suspension means forloading and hauling a typical container in a railway car such as isillustrated in FIGURE 1 of this application. The reference numerals havebeen changed by the addition of the prefix P to avoid confusion with thereference numerals in the present application.

Referring now to the drawings, an inner shell 10 made of a rigidmaterial having a high coeificient of thermal conductivity such as ironor aluminum, is fitted internally with a cellular structur e jgmomprised of support bars 14.

The support bars 14 may be conveniently made of any 3 good thermalconductive metal such as copper. Radioactive material may be placedwithin the openings between the support bars; such a structure isparticularly f convenient when radioactive fuel rods are being shippedwherein each assembly of fuel rods may be inserted with- ,in a cell 12.The support bars 14 conduct thermal heat to the sides 16, 18 of theshell 10, and in turn the support bars 14 are mounted in slots 20provided on the inner surfaces of the side walls 16 and 18. 1

The inner shell 10 is supported by a plurality of heavy webs 22 designedto provide both mechanical support and to conduct thermal energy fromthe side walls 16 and 18 outward toward the outer shell 24. The outershell is comprised of a strong metallic material preferably caibon steelclad with stainless steel having good structural properties and highcoeflicient of heat conductivity and emissivity so that thermal energymay be dissipated by radiation into the surrounding air. The thicknessof the sides 26, 28 of the outer shell need not be nearly so large fromthe standpoint of thermal heat transfer as the walls of the inner shellsides 16 and 18 or the webs 22.

The webs 22, as shown in the embodiment illustrated in FIGURES 1 through4, are positioned diagonally on the edges of the rectangular inner andouter shells 10 and 24 respectively. The various sections of the innerand outer shells and the webs may be joined by heavy weldments; it isimportant that the junctions of the various structural members besmoothly juxtaposed and preferably metallurgically bonded to obtain themaximum heat transfer efficiency.

Between the inner and outer shells there are openings 30 into whichradiation shielding material Such as lead blocks 32, 114 may beinserted. These blocks are tapered and cut diagonally at 36 to providecomplementary halves as shown in the drawings so that when the steel orrigid shell structures expand due to thermal heating there will be noopenings created in the radiation shielding. The blocks 32, 34 arefastened at their thicker ends 32a and 34a to the webs 22. Uponexpansion due to heating the lead blocks move with respect to oneanother along the diagonal cut 36, thus assuring that no radiationleakage path may be inadventently opened between the steel shells andwebs and the lead absorber blocks.

The relative proportions of the webs, the inner shell wall thicknesses,the outer shell wall thicknesses and the spacing between the shells mustbe determined in each instance to satisfy simultaneously the thermalheat transfer conditions and the radiation attenuation conditions. Theradiation attenuation longitudinally through the web section must besuflicient to prevent excessive radiation leakage, and therefore, forany given material selected for the web and thermal heat transfer mediuma minimum length of the web is determined. A wide variety of materialshaving different properties are available with which variouscombinations permit designs of reasonable Weight and dimensions. Table Ibelow tabulates the parameters for some preferred materials.

Table I Gamma Coefficient of Absorption Thermal Con- Coelllcient forductivity, Density, Material Shielding B.t.u./hr. it cmfl/g.

Design (cmr F. at 400 F.

for 1.4 mev. Gammas Iron 39 26 7. 8 Stainless Steel 18-8. 39 10.0 7. 8Lead 63 18 11.3 Concrete. .12 0. 5 2. 3 Tungsten 0.90 83 19.3 Aluminum0. 12 124 2. 7 \Vater 0. 06 0.4 1.00 Copper 0. 42 215 8. 9

Openings must be provided in the container to drain any moisture whichcollects therein and to provide a means for ventilating. It isconvenient to charge the loaded container with helium gas which providesa much better heat transfer medium than air between the radioactivematerial and the walls 16 and 18 of the inner shell 10. These openings46 for the drain, and 4S and 50 for purging with helium must becircuitous so that no direct unobstructed radiation path is provided inthe container. Threaded removable plugs 46a, 48a and 50a are positionedin the respective openings.

The ends of the container are sealed by a removable cover 38 on one endand a fixed end 40 at the other end. If the end enclosures 38 and 40 aremade of the same material as the webs they may conveniently be made asthick as the length of the web sections. The removable cover 38 must beprovided with a recessed seating surface 42 and carefully fitted contour44 so that the closure of the cover on the container will be tight andnot permit openings for the leakage of dangerous radiation. The covermay be secured by means of bolts 38a.

The container is provided with tiunnions 52, two on either side, tofacilitate positioning on a frame or cradle which may be mounted on arailway car. It is necessary to suspend the loaded container so that airfreely passes about all outer surfaces of the container to conduct awaythe considerable quantity of heat emitted by the radioactive contents.

FIGURES 8 and 9 illustrate the cradle and positioning within a railwaycar appropriate to carry the container disclosed herein. A suitablerailway car is shown at P10. It is of the gondola car type with a dropcenter floor structure P12 consisting of longitudinal stringers andcross members as usual, but much heavier due to the unusual loadrequirements. The car is supported upon wheel axle truck assembliesindicated at P14 for operation upon railroad track. Car sides and endsare indicated at P16 and P18 respectively. Extending upwardly and overthe car is a two section removable guard screen P20, but one of suchsections being shown for convenience of illustration. This guard screensurrounds the containers when in the car and protects the public andrailroad personnel from the heat being dissipated therefrom. Rising fromthe floor of the car are four pairs of frame-like saddles P22; two pairsbeing located adjacent the ends of the car, and the other two pairsadjacent the transverse center of the car. Said saddles are spacedtransversely of the car a distance approximating the width of thecontainers as clearly seen in FIGURE 9. The upper extremities of eachpair of saddles are formed into upwardly facing semicircular cradleseats P24 which are axially aligned transversely of the car. The saddlesat one end of the container are pivotally mounted to allow fortemperature expansion of the containers.

The containers themselves are indicated generally at P30, and as beforestated are substantially square in cross section and in length abouthalf the length of the car P10, so that two such containers may beconveniently carried thereon. At opposite sides of each container, neareach end, is provided a laterally extending trunnion having two journalportions, the inner portions P32 for seating within the cradles P24.Upon the outer journal portion of each trunnion P32 is pivotally mounteda lift and tiedown lug P34 by means of which the containers may besecured to the car or lifted therefrom by means of a crane liftindicated at P36.

A second preferred embodiment of my invention is illustrated in FIGUREwhich shows a cut-away perspective view of a circular cylindricalcontainer comprising a circular cylindrical inner shell 54, an outercylindrical shell 56 and a plurality of webs 58 mounted to suspend theinner shell within the outer shell. By providing a greater number ofwebs a greater heat transfer between the inner shell and outer shell isachieved however less radiation attenuation shielding may be obtainedthrough the webs than through the radiation shielding blocks 62positioned in the space 60 between the shells 54 and 56. By the use, forthe webs 58, of a metal containing a high percentage of tungsten whichhas a large coefficient of gamma ray absorption the size of thecylindrical container may be made small and serve its purpose ofproviding both radiation attenuation and means for thermal cooling.

A specific design is described below:

FIGURES 6 and 7 illustrate specific embodiments which have successfullyutilized the broader concept of my invention. Twelve assemblies of aparticular nuclear reactor fuel rod, removed after extensive use withinthe reactor, emit both gamma and beta radiation which produces anintensity of 4.15 X 10 roentgens per hour on the inside surface of thecontainer. At the same time the twelve assemblies produce 73,000 B.t.u.per hour which must be dissipated through the outer shell of thecontainer. The fuel rods are 11 feet 2 inches long, the interior of thecontainer 12 feet 2 inches long.

Referring now to FIGURE 6, the inner shell 70, the outer shell 72 andthe web 74 are made of carbon steel. The web has mean transversedimensions of 18 cm. and as shown in the cross sectional view is 44 cm.long. Both the inner and outer shells are 4 /2 cm. thick. The two shellsare separated by a distance of 21 /2 cm. into which tapered lead blocks76 and '78 have been inserted. The thicker portion of the lead block 76is fastened at 80 to a corrugated surface 82 of the web 74. Coppersupport bars 84 are mounted in slots 86 which have been provided withinthe inner shell 70. The center lines of the copper bars are positioned16 cm. apart on both sides of the squares wherein the fuel assemblies,each comprising twenty five fuel rods, are conveniently positioned. Thedimensions of the outer shell between the inner section thereof with theweb and the center line of the container is 47 cm. By use of thematerials in the configuration described the temperature along thecenter line between the inner wall of the inner shell and the outersurface of the outer shell is approximately 250 F. The maximum radiationintensity about any point on the surface of the outer shell is 5.5milliroentgens per hour.

FIGURE 7 illustrates a cylindrical cask which utilizes the principle ofmy invention. It is adapted to hold twelve assemblies of twenty fivefuel rods each having the heat and radiation properties as specifiedabove in connection with the charge for which the embodiment of FIG- URE6 was designed. The inner shell 90, the outer shell 92 and the webs 94are made of carbon steel. The inner shell radius is 30 /2 cm. Both theinner and outer shell thicknesses are 4 cm.; and the separation betweenthe inner shell and outer shell is 25 cm. The webs 94 are 2 /2 cm.thick, extend longitudinally the full length of the cask and are 38 cm.long. There are twelve webs positioned between the inner and outer shellthrough which thermal energy is conducted from the inner shell to theouter shell. These webs are positioned at approximately a 45 angle tothe radius. Lead absorber blocks 96 are positioned between the inner andouter shells and between each of the webs. The positioning of the websin non-radial orientation assures that the radiation must pass through asubstantial portion of one or more of the lead blocks before it reachesthe outer shell, and thus attenuation is assured. Copper support bars 98are positioned to form squares 16 cm. on the side within the innershell.

The radiation dosage rate at the outer surface of the outer shell doesnot exceed 5.5 milliroentgens per hour. The temperature differencebetween the inner shell and the outer surface of the outer shell alongany radius will not exceed 46 F.

The foregoing description, specifications and drawings are merelyillustrative of my invention, the scope of which is limited only by thefollowing claims.

I claim:

1. A minimum dimension container for transporting intensely radioactivehighly exothermic material comprising an inneuand an outer shell inspaced relationship, spaced diagonally disposed web sectionstherebetween, the shells and web sections being made of high strengthmaterial having high coefficient of heat conductivity and lesser nuclearradiation absorption coefficient, material having high nuclear radiationabsorption coefficient positioned within the voids between the shellsand between 7 adjacent web sections, the width of the Webs being relatedinversely to the radiation absorption coelficient of the web materialsuch that the radiation attenuation through the shells andinterconnecting webs is equal to,

that through the shells and the absorber material whereby heat,isremoved from radioactive material positioned within the inner shell byconduction through the webs and radiation is attenuatedby-the radiationabsorber material in the space between the shells.

2. A minimum dimension container for transporting thermally hot highintensity radioactive material comprising an inner shell of ahighmodulus of elasticity and high coefiicient of, thermal conductivitymaterial with intermediate gamma ray capture cross section, an outershell of material similar in' properties tothe inner shell in spacedrelationship thereto, spaced diagonally disposed web sections positionedbetween the inner and outer shells, the concentric shells in combinationwith the Web sections comprising a means for conductively transportingthermal heat from the interior ofthe inner shell to the exterior of theouter shell, complementary tapered sections of high coefficient of gammaray capture cross section material positioned in the voids between theinner and outer shells and between adjacent web sections mounted to theweb sections at ,the thicker ends, of the taper sections whereby heat isremoved from the inner shell and transported to the ,outer shell fordissipation through the web sections, nuclear radiations are mainlyabsorbed by the high density material in the void between the shells,and by passage longitudinally through the web sections, and wherebythermal expansion of the shells and the resulting relative movement ofthe Webs slides the dense shielding sections with respect to one anothertransversely of thedirect radiation path thereby assuring integrity ofthe radiation shield regardless of the thermal temperature of thevarious parts of the container,

3. A minimum dimension container for transporting intensely radioactive,highly exothermic material comprising an inner and outer shell in spacedrelationship, radial Web sections therebetween, the shells and web beingmade of high strength material with high coefficient of heatconductivity, complementary tapered members of high density nuclearradiation shielding material positioned in the voids between the shells,the tapered surfaces being juxtaposed and the thicker ends of the highdensity members attached to the web sections, whereby the radiationshielding integrity of the container is preserved regardless oftemperature of the component parts of the container, heat is removedfrom the, interior of the inner shell by conduction through the Webs tothe outer surface of the outer shell Where it is dissipated, and theradiation is attenuated by passing through the high density shieldingmaterial or longitudinally through the web sections.

4. A container for transporting intensely radioactive highly exothermicmaterial comprising an inner and outer shell in spaced relationship,spaced diagonally disposed Web sections therebetween, the shells and websections being made of highstrength material having high coefficient ofheat conductivityv and 'lesser'nuolear radiation absorption coefiicient,material having high nuclear radiation absorption coeificient positionedwithin the void between the shells and between adjacent web sections,the Webs being substantially wider than the radial distance of spacingbetween the shells such that the webs are positioned at an angle tothe'rad'ial plane between the shells whereby heat is removed from theradioactive material positioned with-in the inner shell by conductionthrough the webs and nuclear radiation is attenuated by the radiationabsorber material in the space between the shells. 5. A container forradioactive material comprising a metallic insidershell and a metallicoutside shell spaced from said inside shell, solid metallic websconnecting said inside and outside shells, the webs being substantiallywider than the distance between the shells, blocks of a more densematerial than that of the shells filling the space between the shellsand between adjacent Webs, said blocks being diagonally cut to providecomplementary halves so that upon eiipansion, due to heating, saidblocks move with respect to one another along the diagonal cut, thusmaintaining radiation shielding.

6. A container as in claim 5 with fourtrunnions located on oppositesides near the ends for supporting the container in endless andpermanent rotating lugs on the trun-nions to act as lifting lugs andalso as hold-down lugs when resting on the support saddles.

References Cited in the file of this patent UNITED STATES PATENTS2,419,346 Ellis Apr. 22, 1947 2,580,249 Seeley Dec. 25, 1951 2,684,447Gilks July 20, 1954 2,843,754 Costello July 15, 1958 3,005,105 Lusk'Oct. 17, 1960

1. A MINIMUM DIMENSION CONTAINER FOR TRANSPORTING INTENSELY RADIOACTIVEHIGHLY EXOTHERMIC MATERIAL COMPRISING AN INNER AND AN OUTER SHELL INSPACED RELATIONSHIP, SPACED DIAGONALLY DISPOSED WEB SECTIONSTHEREBETWEEN, THE SHELLS, AND WEB SECTIONS BEING MADE OF HIGH STRENGTHMATERIAL HAVING HIGH COEFFICIENT OF HEAT CONDDUCTIVITY AND LESSERNUCLEAR RADIATION ABSORPTION COEFFICIENT, MATERIAL HAVING HIGH NUCLEARRADIATION ABSORPTION COEFFICIENT POSITIONED WITHIN THE VOIDS BETWEEN THESHELLS AND BETWEEN ADJACENT WEB SECTIONS, THE WIDTH OF THE WEBS BEINGRELATED INVERSELY TO THE RADIATION ABSORPTION COEFFICIENT OF THE WEBMATERIAL SUCH THAT THE RADIATION ATTENUATION THROUGH THE SHELLS ANDINTERCONNECTING WEBS IS EQUAL TO THAT THROUGH THE SHELLS AND THEABSORBER MATERIAL WHEREBY